1. Field of the Invention
This invention relates to mechanisms for controllably advancing a rotating cylindrical member and, more particularly, to a mechanism that can be adjusted to accommodate different diameters of rotating cylindrical members.
2. Background Art
It is known to advance rotating cylindrical members, such as sewer cables, through the use of rollers which engage the cable. The rollers are mounted on a frame which has an opening with an axis that aligns with the axis of the cylindrical member to be advanced. The rollers project into the frame opening and define the effective diameter for the frame opening. Normally, the rotational axes of the advancing rollers are simultaneously variable to control the speed, and in some cases the direction, of advancement of the cable. Exemplary advancing mechanisms are shown in U.S. Pat. Nos. 3,394,599 (Tucker) and 3,451,090 (Lo Presti et al).
One drawback with some conventional mechanisms for advancing a rotating cylindrical member is that the mechanism is suitable for only a single diameter of cylindrical member. To obviate this problem, structures have been developed to permit a single mechanism to accommodate more than one diameter of cylindrical member. One such structure employs a plurality of shims captively held between a frame cap and a frame body on the mechanism. The cap abuts a mounting block which carries the advancing roller. The mounting block is mounted to the frame so that it and the advancing roller thereon are movable towards and away from the axis of the opening in the frame through which the cylindrical member extends. By adding shims, the distance of the cap from the frame opening axis is increased, which allows the mounting block, with the roller thereon, to move further away from the frame opening axis than it can in the absence of the shims. By so doing, the diameter of the cylindrical member that the mechanism will accommodate is increased. Similarly, by removing the shims, the cap is moved inwardly towards the frame opening axis so that the maximum diameter of cylindrical member that the mechanism will accommodate is reduced. In a typical mechanism, three mounting blocks with advancing rollers are provided on the frame and equidistantly spaced around the periphery of the frame opening. Each cap may be held in place by four bolts. Since all caps must be simultaneously adjusted to change the cable capacity for the advancing mechanism, the user must remove twelve bolts, remove or add shims, and replace the bolts. This is not only an inconvenient operation, but it is also very time consuming. If for any reason the wrong number of shims are added or removed, the entire procedure must be repeated.
Another prior art structure that is used to vary the cable capacity for the advancing mechanism also employs a removable frame cap. The cap is bolted to the frame body so as to be removable therefrom. A rectangular blocking wall is in turn removably bolted to the cap. The blocking wall is selectively bolted in one of two different positions. In one position, the longer cross-sectional dimension acts between the cap and the advancing roller mounting block. In the other position, the shorter cross-sectional dimension acts between the mounting block and the cap. In the former position, the mounting block and advancing roller are urged closer to the frame opening axis than in the latter position. There are several drawbacks with this structure. First of all, not only must the cap be removed, as required with the previously described structure, but the blocking wall must be additionally unbolted from, repositioned and reattached to the cap. This is also a time consuming and inconvenient operation. Additionally, the surface that abuts the mounting block may over time become worn. The result of this is that the mounting block may not be stably and consistently maintained in the positions required to accommodate different diameters of cylindrical members.
Tucker (U.S. Pat. No. 3,394,599) discloses advancing roller mounting blocks that are spring biased inwardly towards the frame opening axis. While the tension on a cylindrical member within the frame opening may be altered with Tucker's disclosed structure, the mounting blocks and advancing rollers thereon are only positively prevented from moving outwardly from only one position; that being when the roller supporting yoke encounters the rigid frame body.
Another problem with prior art mechanisms is that it is difficult to initially direct the cylindrical member into the frame opening, as from one side of the frame on which a cable holding drum is provided to the other side of the frame to which the cable is to be advanced. Typically, sewer cables have a free end with a bore extending therethrough angularly oriented with respect to the length of the cable. It is common in the prior art for the user to direct a screwdriver or other pointed object into that bore and then to push the cable into the frame opening from the drum side of the frame. The user can assist this operation by threading the cable through by hand from the drum side of the frame. Depending upon the configuration of the device and the proximity of the drum to the advancing mechanism, threading of the cable may be a very awkward procedure.